This application is related to Japanese Patent Application No. HEI11(1999)-189201 filed on Jul. 2,1999, whose priority is claimed under 35 USC xc2xa7 119, the disclosure of which is incorporated by reference in its entirety.
1. Field of the Invention
The present invention relates to a method of forming a metal film or a silicide film in which the content of a halogen element is reduced and a film formed by the method. More particularly, the invention relates to a method of forming a metal film or a silicide film which has a reduced content of a halogen element, by use of a deposition apparatus having received a particular pretreatment, and a film formed by the method.
2. Description of Related Art
As halogen-containing films, known are WSi films which are used for gate electrodes of transistors (polycide films of WSi/polysilicon), for example. It is known that, in a polycide film produced by a conventional WSi film forming technique, oxidation is liable to take place at the interface between a WSi film and a polysilicon film due to fluorine in the WSI film during a thermal treatment step after the formation of the WSi and polysilicon films, and also that similar oxidation is liable to take place on sides of the WSi film after etching of the WSi and polysilicon films. To put it in further detail, the WSi film constituting the polycide film contains fluorine therein because the WSi film is usually formed by reaction of a SiH4 gas with a WF6 gas. Fluorine contained in the WSi film cuts a Sixe2x80x94O bond in a gate oxide film formed below the polycide film and substitutes for O atom. Cut-away O atoms react with a polysilicon film on the gate oxide film to form SiOx. Thus oxide films are formed at the WSi-polysilicon interface or on the sides of the WSi film. This is referred to as abnormal oxidation hereinafter.
To cope with this problem, Japanese Unexamined Patent Publication No. HEI 9(1997)-213942 proposes introduction of nitrogen into the gate oxide film. According to this publication, because nitrogen introduced into the gate oxide film combines strongly with silicon or oxygen in the gate oxide film, fluorine cannot cut the Sixe2x80x94O bond in the gate oxide film. Therefore, the above-mentioned abnormal oxidation can be inhibited. However, the WSi film formed by this technique has the possibility of abnormal oxidation in positions other than the gate oxide film.
Also proposed is a method of forming a SiO2 film and a Si3N4 film as oxidation protection films on the top and sides of the WSi film in production of the polycide film of WSi and polysilicon thereby to prevent a direct oxidation of the WSi film under high temperatures. However, with this method, the abnormal oxidation takes place at sides of the WSi film after the etching of the WSi and polysilicon films.
Further, Japanese Unexamined Patent Publication No. HEI 2(1990)-218164, taking notice of stress of the WSi film, proposes a method of depositing a Pxe2x80x94Si3N4 film on the polycide film of WSi and polysilicon to offset the stress of the WSi film and selectively oxidize the sides of the polycide film using the Pxe2x80x94Si3N4 film as a mask to form sidewall films. With this method, improvement can be made with regard to the stress of the WSi film. However, as shown in FIG. 3, the abnormal oxidation may occur at an interface 10 between the WSi film on the sides of the polycide and the sidewall oxide film because the fluorine content in the WSi film is not controlled.
Japanese Unexamined Patent Publication No. HEI 8(1996)-186256 proposes a method of forming a SiO2 film, a Si3N4 film and the like on the top and sides of the polycide film of WSi and polysilicon to prevent exfoliation of the WSi film (see FIG. 4). However, with this method, there is a problem in that cracks take place in the WSi film if a rapid thermal treatment is conducted at a high temperature of 800 to 900xc2x0 C. for forming the SiO2 film.
With the above-described conventional methods of forming the WSi film, the actual situation is that there still occur the abnormal oxidation of the WSi film, especially abnormal oxidation at the sides of the WSi film after the etching of the WSi and polysilicon films, and cracks and film exfoliation in the WSi film at the forming the polycide film of WSi/polysilicon.
Accordingly, in view of this situation, an object of the present invention is to provide a method of forming a film containing a halogen element in a reduced content, for preventing the abnormal oxidation, exfoliation and cracking of the film, and a film obtained by the method.
With the intention of solving the above-mentioned problems, the inventors of the present invention have paid attention to conditions for pretreatment of a deposition apparatus. Usually, before deposition is carried out, the deposition apparatus is cleaned by a cleaning gas passed through the deposition apparatus to remove residual substances of a gas used for the previous deposition and dust resulting therefrom. Or after cleaning, the apparatus is often left under a reduced pressure for a long time, and thereafter an idle deposition is sometimes conducted. Unexpectedly, the inventors have found out that the content of a halogen element in a film can be effectively reduced if the film is formed by a deposition apparatus having had an idle deposition within a certain time period after cleaning and have accomplished the present invention.
The present invention provides a film forming method comprising forming a metal film or a silicide film in which the content of a halogen element is reduced, with use of a deposition apparatus which is cleaned by passing a cleaning gas therethrough and subjected to an idle deposition using a material for the intended metal or silicide film within 24 hours after cleaning.
The present invention also provides a WSi film formed by the above-described method whereby the fluorine content is reduced to 4xc3x971016 atms/cm3 or less.
These and other objects of the present application will become more readily apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.